Apparatus for handling molten magnesium and its alloys



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APPARATUS FOR HANDLING MOLTEN MAGNESIUM AND ITS ALLOYS Clarence A. Pippin,

Midlad, Mich., assinor to The Dow Chemical Company,

Midland, Mich.,

a corpo'ation of Delaware Application October 11, 1947, Serial No. 9,333 3 Claims. (Cl. 103-87) The invention relates to apparatus for handling molten magnesium and its alloys and is particularly useful in the foundry for trans- Ierring the molten metal from a -body thereof in a melting vessel, for example, to another location, such as a casting mold It more particularly concerns an apparatus comprising a pump and associated parts in a combination which is especially useful as a portable device for transferring the molten metal from a melting furnace, pot, or the like, without withdrawing contaminants from the melt along with the withdrawn metal.

The ease with which molten magnesium and its alloys are attacked by the atmosphere is well known and special measures must be taken to protect the molten metal during the conventional operations with these metals such as those in the foundry. The usual method of protecting the molten metal in a melting vessel; or the like, is to cover the exposed surface with a suitable fiux. such as magnesium chloride mixed with an alkall metal chloride. The presence of the flux as well as dross formation, which occurs in spite of the usuai precautions to prevent atmosphere attack on the metal, makes it diflicult, if not impossible at times, to withdraw and transfer clean metal from a fluxed body thereof to another location as a mold.

Heretofore molten magnesium and its alloys have been handled and transferred generally in batches carried in crucibles or ladles. Attempts to pump the molten metal as a means of transfer'ring it from place to place, as in foundry Operations, have not been wholly satistactory with available pumping apparatus. This I have found causes contaminants to be dispersed in the melt and also entrainment of contaminants in the metal being transferred.

The principal object of the present invention is to provide an apparatus of the type indicated but which does not cause contamination o! the metal and can be operated easily to transfer molten metal from place to place without entraining therein contaminants. Other objects and advantages will appear from the following description of the invention taken with the accompanying drawing.

In the drawing, the single figure is an elevation, largely in cross section, of a preferred form of the apparatus.

Referring to the drawing in detail, the appa-' ratus of the invention, designated generally by numeral i, is shown Suspended from a hook 72 in a melt 3 contained in the melting pot l. 'The' meiting pot 4 is supported in the Iurnace setting 2 5 and heated by the burner I. The pot. fumace setting, and burner are conventiona and not a part of the invention. As shown, the apparatus comprises a centrifugal pump, designated generally by numeral 1, built in the lower portion of the apparatus. The pump 'I consists of a rotor, having vanes 8 mounted upon the plate 9, which-is secured to the lower end of the drive shaft to and operates within a housing. This consists of a cylindrical casing ll covered at the upper end with the plate z and at the lower end with the piate !3. The upp r' plate I! has an opening I 4 in which is secured the bushing I! which forms the hearing fur the lower end ph y.

of the drive shaft o. The lower plate ll is provided with a central opening s which serves as the inlet to the pump. The pump has a discharge outlet ll in the wall of the casing ll.

The drive shaft o, which extends upwardly well above the depth of molten metal in which the pump is to operate, is surrounded in part by a shroud a. As shown, the shroud ll is a tubular member which extends'nearly the full length of the shaft Ifl. The lower end of the shroud is secured, as by welding, to the upper end of the pump casing ll and prcferably forms a contlnuation thereof. A hood s, preferably 'of conical'shape. has its upper edge' :e secured to the shroud ll. its lower edge or periphery 2l` preferably approx'imately on a level with the pump inlet li and has a diameter preferably between about 3 and 5 times that of the pump rotor. The under surface 22 oi' the hood, which slopes upwardly from the' pemakes an angle, a, with the horizontal of not lessthan about about to The shroud s just above the upper plate i! is provided with an opening 23 which permits molten metal to enter the shroud when the apparatus is immersed in the melt and to drain when the apparatus is removed from the melt.

Another opening, 24, is provided in the shroud just under the top of the hood, if the under side is steepy sloping, for permltting the passage into the shroud of any gas that may be trapped in the space 25 under the hood when the apparatus is lowered into the melt. I

An opening 26 in the shroud above the molten metal level is connected to a source (not shown) of inert gas such asargon or helium by a pipe 21. A vent!! closable by -valve !I is .shroud. V

` On -the' upper end u of the shroud, there is 5. A preferable angle is provided in the secured the coverplate sa having an og 32 slightly larger than the upper end oi the drive shaft l e which extends through, the opening, The v cover plate ei-carries the thrust hearing 33 which a baii ai is secured to the brackets se and .carries a ring 38 by which the apparatus may be Suspended from the hook 2.

A delivery pipe 39 is connected to the discharge outlet li of the pump and has its upper portion ee held by a -bracket M mounted on the cover plate 38. for the pipe may be provided, for example the outlet 62, which is arranged to discharge moiten metai'into the mold &13, for example, placed beneath the outlet. i

The lower hearing advantageously may be made of cast iron while other parts of the apparatus which come in contact with the moiten metal may be made preferabiy of mild steel, aithough some other metals may be used ii desi'ed.

In operation, the apparatus is intrcduced into the body oi the melt to .be transferred, while inert gas is supplied to the shroud and the valve 29 is open to vent the shroud and permit displacement of -air therefrom by the inert gas and molten metal which enters through ports 23 and ze. In introducing the apparatus into the melt, the flux on the surface of the melt is first parted (as in conventionai ladling'practice) so as to expose as clean a surface of metal as possible through which to pass the pump and hood IQ.

' shaft penetrates the surface of the melt at t. As

Any suitable form of delivery outlet thereby to avoid flux contamination of the pump,

shroud, and under surface 22 of the hood.

The apparatus is Suspended from the -hook 2, as exemplified in the drawing, in the melt at a level where the pump inlet lt is well above the top of the body of settled sludge t. After the air in the shroud has been replaced by the inert gas and moltenmetal, the valv'e 29 is closed. During operation, some inert gas may escape through the opening 32 and thrust hearing 33 unless this is gas tight. clusion of the air from the shroud is readily accomplished in spite of such leakage by providing a constant flow of inert gas into the shroud.

The motor 34 is operated so as to turn the rotor assembly'at a speed to suit the 'rate of metal flow desired from the outlet 40. I have found. for example, that with a rotor 7 inches in diameter having four'equally spaced vanes inch wide revolving -at about 250 R. P. M. in a housing, clearing the rotor by /e inch, about 40 pounds of molten magnesium or magnesium-base alloy is pumped per minute against heads of a few feet through a inch delivery pipe.

The length of the drive shaft o should be sufficient to permit the motor 34 to be mountd well above the molten metal body so that reasonably cool operation of the motor is had. I have found that by using a compressed air driven motor, it may be operated satisfactorily about .1.5 to 2 feet or more above the top of the melt without overheating. Since the usual depth of. the 'molten metal maintained in conventionai meiting practice does notexceed about 2 to 4 feet. the drive Howeven complete ex- 'a consequence, the revoiving drive shaft operates the pumponlyin clean molten metal free from flux and products of oxidation of the moiten metal. Therefore, flux and products of oxidaton are not dispersed inthe melt as a result of operating the `pump.` Furthermore, as the moiten meta! has free access to the interior of the shroud through the openings 23 and ai therein, the bushing se is always submerged in molten metal which acts as a seal for the drive shaft obviating the need for a stuming box on the drive shaft entering thepump housing.

In addition, the conventional foundry fiuxes, as is well known, creep over the surface of the ferrous metals usually used for the construction of ladling apparatus and convention'al pumping apparatus. With thepresent apparatus, the hood on the shroud substantially obviates flux contamination due to creeping of fiux, for any flux which may creep down the outside of the shroud and hood from the surface of the melt is deterred from ever reaching the pump inlet because the flux does not creep upwardly along the upwardly sloping underside of the hood.

Among the advantages of the invention are that molten magnesium and its alloys may be safely transferred from a fiuxed body thereof without withdrawing flux or other contaminants with the withdrawn metal; the rate of with- .drawal is easily regulated from a small to a great let on the lower side; a drive shaft having its lower end secured to the rotor and of sufiicient length for the upper end to extend above the surface of the melt; a shroud for the drive shaft extending from the pump to near the upper end 'of the drive shaft; a cover plate on the upper end 'of the shroud having an opening therein through which extends the drive shaft; a thrust hearing for the upper end of the drive shaft carried by the cover plate, 'said hearing being adapted to carry the thrust of the shaft; a hearing for the lower end of the drive shaft in the lower end of the shroud above the pump; a motor secured to the cover plate and coupled to the drive shaft for driving the same; a -hood for the pump surrounding the shroud, said hood having its under surface soping upwardly from the periphery toward the shroud and its periphery extending outwardly from the pump, said shroud having an opening under the hood communicating between the in,- side and outside of the shroud, and said shroud being adapted, when the hood is immersed in the melt, to maintain an inert atmosphere around the shaft above the melt and prevent flux from' reaching the surface of the melt in contact with the shaft 'need not be over about 4 too feet long. {(6 shaft.

2. An apparatus for transferring molten magnesium and alloys thereof from a tiux covered melt thereof which comprises a centrifuga pump having its rotor horizontally disposed and its inlet on the lower side; a drive shai't having its lower end secured to the rotor and of sumcient length for the upper end to extend above the surface of the melt; a shroud i'or the drive shaft extending from the pump to near the upper end of the drive shaft; a cover plate on the upper end of the shroud having an opening therein through which extends the drive shatt; a thrust hearing for the upper end of the drive shait carried by the cover plate, said hearing being adapted to carry the thrust of the shat; a hearing !or the lower end of the drive shaft in the lower end oi the shroud above the pump; a motor Secured to the cover plate and coupled to the drive shatt i'or driving the same: a hood !or the pump surrounding the shroud, said hood having its under surface sloping upwardly from the periphery toward the shroud and its periphery extending outwardly from the pump; said shroud having an opening under the hood communicating between the inside and outside of the shroud, and said shroud being adapted when the hood is immersed in the melt to maintain an inert atmosphere around the shaft above the melt and prevent flux from reaching the surface of the melt in contact with the shatt; and a pipe connection on the shroud for admission of inert gas thereto.

3. An apparatus for transfer-ring molten magnesium and alloys thereof !rom a flux covered melt thei-eci' which comprises a centrifuga pump 'through which extends the drive shaft; a thrust hearing carried by the cover plate for the upper end of the drive shaft, said hearing being adapted to carry the thrust oi' the shaft; a. hearing for the lower end of the drive shaft in the lower end of the shroud above the pump; a motor Secured' to the cover plate and coupled to the drive shaft for driving the same; a hood !or the pump surrounding the shroud, said hood having its under surface sloping upwardly from the periphery toward the shroud and its periphery extending outwardly from the pump; said shroud having an opening under the hood communicating between the inside and outside oi' the shroud, and said shroud being adapted, when the hood is immersed in the melt, to maintain an inert atmosphere around the shaft above the melt and pre vent flux from reaching the surface of the melt in contact with the shaft; a. pipe connection on the shroud for admission oi' inert gas thereto; and a valved vent on the shroud adapted to be opened or closed by a valve.

CLARENCE A. PIPPIN.

No references cited. 

